Vacuum tube filament structure



" J ly 11, 1933. F, s. MCCULLOU H 1,917,991

VACUUM TU BE FILAMENT STRUCTURE Original Filed Sept. 16. 1922 Fig.2.

WITNESSES: lNVENTOR Fredemck iM Cullough 3 ATTORNEY Patented Jul 11, 1933 UNITED STATES PATENT OFFICE FREDERICK S. MCCULLOUGH, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WEST- I'N'GHOUSE ELECTRIC -& MANUFACTURING COMPANY, A CORPORATION OF PENN- SYLVANIA VACUUM TUBE FILAMENT STRUCTURE Application filed September 16, 1922, Serial No.-588,558. Renewed November 9, 1928.

My invention relates to evacuated electric devices, having particular relation to the cathode structures of such devices.

An object of my invention is to provide 5 a cathode especially designed for use in power tubes which is of unusual rigidity and strength of construction and which lends itself to inexpensive quantity-production methods of manufacture.

Another object of my invention is to provide a cathode, whereby a thin, fragile, oxidecoated element may be employed in highvoltage, high-power tubes, wherein heavy electrostatic forces obtain between the oathode and the other elements of the tube.

Another object of my invention is to provide a cathode of improved design, whereby heavy electron emissions may be obtained with extremely low energizing currents.

In the construction and operation. of a power tube, it has, heretofore, been customary to employ a single electron-emitting element which may or mziy not be provided with an oxide coating. 11 order to obtain the necessary electron emission from a cathode of the above-mentioned character, it has been necessary to operate the same at as high temperatures as possible, thereby necessitat-.

ing a heavy exciting current, and greatly shortening the life of the tube.

According to my invention, I provide a cathode embodying a construction for carrying the above indicated desired results into effect. Very briefly, the cathode comprises a supporting element and a fragile, oxidecoated element which is wound around said supporting element and supported thereby.

With these and other objects in view, my invention further consists in the details of construction and arrangement hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Figure 1 is a front elevational view, shown partially in section, of a vacuum-tube device embodying my invention; and

Fig. 2 is an enlarged detail view of the cathode construction embodying my inven-.

tion, with the oxide-coated element partly unwound from the supporting element.

In the illustrated embodiment of my invenmounted in the press 4. The carrier rods 7 and 8 may be extended through the press 4 by means of external connectlons 9 and 11, which are electrically connectedthereto.

A helical grid element 12 is symmetrically disposed about the cathode 6 and may be supported by means of a carrier rod 13 which is mounted in the press 4. The carrier rod 13 may be extended through the press 4 by means of a connection 14 to provide an external connection for the grid 12.

A cylindrical anode element 15 is symmetrically disposed with respect to the aforementioned elements and is supported by carrier rods 16 and 17 which are also mounted 1n the press 4. One of the carrier rods, as 16, may be extended through the press 4 to pro yi5de an external connection 17 a for the anode The cathode structure 6 comprises a central core member or rod 18 and a fragile oxide-coated metallic strip 19, which is spirally wound around the core member 18 and supported thereby. Adjacent ends of the core member 18 and of the strip 19 are welded together near the connection with the supporting rod, thereby connecting the core 18 and the strip 19 in parallel relation at opposite ends.

The central core 18 may be of any material which is easily degasified and which is capable of withstanding the heavy electrostatic forces peculiar to power-tube constructions. In actual practice, I have found that a rod of tungsten is very satisfactory. The fragile metallic strip 19 may correspond in strength to the cathode elements of small receiving tubes wherein a thin strip of platinum iridium having an oxide coating is usually employed. It is noted that the different elements or sections constituting the cathode structure 6 have different emissivities. The

strip has a higher specific resistance than the rod of tungsten.

The core member 18 is so designed that, when the fragile metallic strip 19 is heated to its normal operating temperature, the tem perature of the rod 18, caused by the heating effect of the currents passing therethrough, will correspond to that of the metallic strip 19, thereby preventing a trans.- fer of heat from the strip 19 to the rod 18.

As previously pointed out, one advantage of my invention is the provision of a cathode of simple but rugged construction which is especially well adapted for high-power transmitting tubes employed in wirelesstransmission systems. Another advantage of my invention is the provision of a cathode requiring extremely small energizin currents to provide the necessary plate-fil ament currents.

While I have shown only one embodiment of my invention in the accompanying drawing, it is capable of various changes and modifications without departing from the spirit thereof and I desire that only such limitations shall be imposed thereon as are specifically set forth in the appended claims or demanded by the prior art.

I claim as my invention:

1. A filamentary member comprising a conductive supporting rod and a relatively fragile oxide-coated strip having a higher specific resistance wrapped therearound, the relative conductivities and dimensions of said rod and said strip being such that when they are energized in parallel the rod shall be heated to a temperature not substantially lower than the temperature of said electronemitting element when the latter is heated to thermionic activity.

2. A cathode structure for use in electricdischarge devices comprising a tungsten rod and a relatively fragile conducting strip wrapped therearound, the said strip being thermionically active at a lower temperature than the supporting rod, the relative conductivities and dimensions of said rod and strip being such that, upon being energized in parallel, the rod shall be heated to a temperature not substantially lower than the temperature of said strip when the latter is heated to thermionic activity, whereby electrons emitted from said cathode structure, when energized, are predominately from said strip and heat does not flow from said strip to said rod.

3. A cathode structure for use in electricdischarge devices comprising a conductive rod and a relatively fragile conducting ribbon so wrapped therearound that the edges of said strip are in contact with one another throughout the helix formed thereby, the said ribbon comprising a material that is thermionically active at a lower temperature than the supporting rod, and the relative conductivities and dimensions of said rod and strip being such that, upon being energized in parallel, the rod shall be heated to a temperature not substantially lower than the temperature of said strip when the latter is heated to thermionic activity.

4. A cathode structure for use in electricdischarge devices comprising a supporting core and a' relatively fragile conducting strip having a higher specific resistance wrapped therearound, said conducting strip being capable of emitting electrons at a lower temperature than said core, and the relative conductivities and dimensions of said core and said strip being so related that, when they are connected in parallel to a suitable potential source, the rod shall be heated to a temperature that is substantially the same as the temperature of said stri when the latter is heated to thermionic activity.

5. A cathode structure for use in electrondischarge devices comprising an electricallyconducting heating element, an electricallyconducting strip 0 higher specific resistance wrapped upon said element, a material of lower conductivity than either said element or said strip, said material being located between, and in contact with, said element and said strip, said element and said strip being electrically connected in parallel.

6. A cathode structure for use in electrondischarge devices comprising an electricallyconducting heating element, and an electrically-conducting strip of higher specific resistance wrapped upon said element, a ma-- terial of lower conductivity than either said element or said strip, said material being positioned in the form of a coating around said strip and comprising an oxide which is thermionically active at a lower temperature than either said element or said strip.

7 A cathode structure for use in electrondischarge devices comprising an electricallyconducting heating element, and an electrically-conducting strip of higher specific resistance wrapped upon said element, a material of lower conductivity than either said element or said strip, said material being located between, and in contact with, said element and said strip and comprising a layer of thermionically emissive oxide.

8. A cathode structure for use in electrondischarge devices comprising an electricallyconducting supporting and heating rod, an electrically-conducting element of higher specific resistance surrounding said rod, a coating of material surrounding said electrically-conducting element, said material having a lower conductivity than either said rod or said electrical-conducting element and being thermionically active at a lower temperawith, and a substance of high electron emitting capacity comprising an oxide applied to said wire.

12. An incandescent cathode comprising a core consisting of tun sten, a platinum wire helically wound on t e core so as to be in electrical contact therewith, and a substance of high electron emitting capacity comprising an oxide applied to said wire.

In testimony whereof, I have hereunto subscribed my name this 12th day of September,

FREDERICK s. McGULLOUGH. 

